About 20 years ago, the United States and a few other countries started using a different pertussis vaccine than had been used previously. The change was in response to public fear about some very rare neurological disorders that may or may not have had a relationship to that older vaccine (it couldn't ever be proven one way or the other).

The vaccine we use today was created to get around any possible mechanism for those disorders and, along the way, ended up having lower rates of the less-troubling (and far, far more common) sort of side effects, as well. Think short-term redness, swelling, or pain at the site of injection.

The downside, reports Maryn McKenna, is that this new vaccine might not be as effective as the old one. In fact, scientists at the Centers for Disease Control, Kaiser Permanente Medical Center in San Rafael, Calif., and Australia's University of Queensland’s Children’s Medical Research Unit, are raising the possibility that a less effective vaccine could be part of why we're now seeing a big increase in pertussis outbreaks.

In the most recent research, a letter published Tuesday night in JAMA, researchers in Queensland, Australia examined the incidence of whooping cough in children who were born in 1998, the year in which that province began phasing out whole-cell pertussis vaccine (known as there as DTwP) in favor of less-reactive acellular vaccine (known as DTaP). Children who were born in that year and received a complete series of infant pertussis shots (at 2, 4 and 6 months) might have received all-whole cell, all-acellular, or a mix — and because of the excellent record-keeping of the state-based healthcare system, researchers were able to confirm which children received which shots.

The researchers were prompted to investigate because, like the US, Australia is enduring a ferocious pertussis epidemic. When they examined the disease history for 40,694 children whose vaccine history could be verified, they found 267 pertussis cases between 1999 and 2011. They said:

"Children who received a 3-dose DTaP primary course had higher rates of pertussis than those who received a 3-dose DTwP primary course in the preepidemic and outbreak periods. Among those who received mixed courses, rates in the current epidemic were highest for children receiving DTaP as their first dose. This pattern remained when looking at subgroups with 1 or 2 DTwP doses in the first year of life, although it did not reach statistical significance. Children who received a mixed course with DTwP as the initial dose had incidence rates that were between rates for the pure course DTwP and DTaP cohorts."

A key thing to remember: This is a nuanced theory that may or may not turn out to be right. But, if it does turn out that this vaccine isn't as effective as we want it to be, that's not a dark mark against vaccines, in general. Sometimes, medicine doesn't work as well as intended. It's a risk of medicine. And the fact that it's major research institutions pointing this possibility out, should give people some comfort in the scientific process. If doctors and organizations who promote childhood vaccination are all in the pockets of an evil conspiracy then there would be no reason why they'd ever do research like this, or talk about it publicly.

Here's a fascinating study that shines a bright spotlight of nuance on some of those maybe-too-simplistic assumptions we make about evolution, physical characteristics, and reproductive fitness.

If you've paid any attention to reporting on the science of what humans find attractive and why, you won't be surprised to learn that studies consistently show that deeper voices are associated with stereotypically manly-man characteristics such as hairier bodies and taller height, that men with these voices and characteristics are judged as being more attractive, and that deep-voiced dudes seem to get more action from more ladies.

Based on all of that, you might be tempted to speculate that a deeper voice is an outward sign of how fertile and virile a dude is and that ladies have evolved to be attracted to that show of baby-making prowess. And that makes sense ...

Except that men with deep voices also seem to have lower-quality sperm. At the Anthropology in Practice blog, Krystal D'Costa explains:

These assessments aren’t entirely made up. There is evidence that secondary sexual traits can predict health and fertility of a partner. Brilliant colors and showy displays have long been natural indicators of potential sexual fitness. For example, deer with bigger, more complex antlers also have larger testes and more motile sperm. Lower frequency sounds have been linked to larger body size across all primate species

However, semen analysis reveals that men with deeper voices have lower scores on seven motility parameters (7)—even when the lifestyle and environmental factors are accounted for. While men with deeper voices may have more sexual partners, they seem less prepared to pass on their genes. Researchers believe the lower sperm quality reflects a trade-off that comes with having to compete for mates:

“Animals have finite resources to partition amongst reproductive activities, and the theoretical models of sperm expenditure assume a basic trade-off between male investment in attracting mates and in gaining fertilizations. Recent studies of non-human animals are providing empirical evidence for this basic life-history trade-off. A number of studies have also reported short-term declines in semen quality associated with social dominance."